The purpose of this research is to continue our study of a group of children with abnormalities of the sex chromosomes who were identified in a cytogenetic survey of 40,000 consecutive births from 1964-1974. This patient group offers the opportunity for study of genetic, developmental, physical and psychological factors in these complex conditions. Our long-term objective is to define the ultimate prognosis for each of these conditions--47,XXX; 47,XXY; 47,XYY; 45,X and mosaicisms of these. Some, but not all, individuals with these karyotypes will have intellectual, emotional or social problems in later life. The data will be analyzed by comparisons between subgroups and by using normal siblings as controls. Previous study of this group of children makes it possible to focus the investigation during childhood on particular facets of vulnerability, and during adolescence on relative changes from previous growth, endocrine and behavioral status. By following the development and by therapeutic intervention, including endocrine where indicated later irreversible pathology may be prevented or ameliorated.